FIG. 4 is a longitudinal section showing one example of the gas turbine of the prior art; FIG. 5 is a partially enlarged longitudinal section of the same gas turbine; and FIG. 6 is an enlarged view of a V portion of FIG. 5. In these figures: reference numeral 12 designates discs of a rotor; numeral 13 a bolt jointing the individual discs; numeral 14 teeth for engaging the adjoining discs; numeral 15 annular arms mounted on the opposed portions of the adjoining discs; numeral 16 a sealing plate mounted between the paired arms; numeral 17 an air passage formed in the discs; numeral 18 an air inlet; numeral 19 a cooling air inflow; numeral 20 flows of the cooling air between the discs.
In the ordinary gas turbine, a plurality of discs 12 having moving blades 11 embedded thereon are axially juxtaposed and fastened by the bolt 13 to construct a rotor, and their joint faces form teeth 14 so as to correspond to bevel gears having an apex angle of 180 degrees and are engaged to transmit a torque and to align the discs. Each disc has the air passage 17 through which the air flow 20 is fed to cool the discs 12 and the roots of the moving blades 11.
FIG. 6 presents diagrams for explaining the working of the teeth 14 formed in the disc 12. FIG. 6 presents a longitudinal section of the disc at (a), a section B--B of (a) at (b), and a section C--C of (b) at (c). FIG. 6 illustrates at (b) and (c) a disc-shaped grinding stone 25 for cutting the teeth 14. Reference numeral 26 designates tooth generating faces formed on the grinding stone. Reference letter H designates the distance between the teeth 14 and the arm 15, and letter R designates the radius of the grinding stone 25.
In order to minimize the wear for one grinding cycle thereby to keep the accuracy, the grinding stone 25 is generally exemplified by a radially large disc-shaped grinding stone 25, the radius of which is larger than the distance H between the teeth 14 and the arm 15. The protrusion of the arm 15 has to be so high as not to obstruct the rotation of the radially large grinding stone.
FIG. 7 is an enlarged view of the tips of the arms of the paired discs, i.e., the V portion of FIG. 5. In order to keep the radially large grinding stone away from contact with the end face 15a of the arm while the tooth generating face 26 of the radially large grinding stone is turning to cut the dedendum of the tooth 14, the arm end face 15a is retracted from a pitch line 21 by a size corresponding to a stone relief 22. This establishes a clearance corresponding to at least a clearance 23 between the end faces 15a of the paired arms. The aforementioned sealing plate 16 is provided for preventing the cooling air from flowing out of the clearance to the outer circumference and is a cover for sealing the clearance between the two end faces of the paired arms. This sealing plate 16 is fitted in the grooves which are formed in the opposed end faces 15a of the arms 15. The sealing plate 16 takes a ring shape, after mounted, by preparing the ring with halves or quarters for the working conveniences and by fitting them individually.
Other examples of the prior art are described with reference to FIGS. 9 and 10.
In the example shown in FIG. 9, cooling air 41 having passed a stator blade 40 flows, as indicated by arrows, out of a hole 42 formed in the upstream side of the inner end of the stator blade 40, and is fed through a labyrinth 43 at the apex of the stator blade to the blade root 45 of a moving blade 44 so that it may be used for the cooling purpose.
That is, in this type, the flow of the cooling air to the blade root 45 depends upon the difference in the static pressure between the upstream and downstream sides of the blade root 45. This makes it necessary to raise the static pressure upstream of the moving blade 44 or to lower the same downstream of the moving blade 44.
In the other type shown in FIG. 10, there is added to the foregoing construction of FIG. 9 a nozzle 46 which is opened in the inner circumference of the stator blade 40 and directed downstream, so that the cooling air may be easily fed to the root 45 of the moving blade 44 by injecting it additionally from the nozzle 46.
The flow of the cooling air to be injected from the nozzle 46 is shown at (b) in FIG. 10 presenting a D--D section of (a) of FIG. 10. If the nozzle 46 has an injection angle (,the moving blade 44 has a circumferential velocity u, and the cooling air has an injection velocity c, a velocity triangle can be formed, as shown at (b) in FIG. 10, to determine an inflow velocity w.
However, although this inflow velocity w is summed, in this type, the flow of the cooling air to be fed to the blade root 45 is also based on the static pressure difference between the upstream and downstream sides at the root 45 of the moving blade 44.